Pyridine N-oxide Research Articles

Deoxygenation of Pyridine N-Oxides in Water at Room Temperature Using TiO2 Photocatalyst and Oxalic Acid as a Clean Hydrogen Source

Amine oxide deoxygenation is an important process for the synthesis of nitrogenous aromatic compounds and de-protection of amine compounds; however, precious metals, organic solvents and undesirabl...

Molecular structure and electron distribution of 4-nitropyridine N-oxide: Experimental and theoretical study of substituent effects

The molecular structure of 4-nitropyridine N-oxide, 4-NO2-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH3-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing –NO2 group in para-position of 4-NO2-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating –CH3 group in 4-CH3-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).

Efficient H2O2 generation and spontaneous [rad]OH conversion for in-situ phenol degradation on nitrogen-doped graphene: Pyrolysis temperature regulation and catalyst regeneration mechanism

H2O2 is a green and valuable chemical that can be electrochemically synthesis from oxygen reduction, offering in-situ application for organic pollutants removal in environmental remediation. However, how to improve activity and further convert into powerful radicals is a still challenge. Herein, we show a facile and general approach to fabricate nitrogen-doped graphene (N-GE) catalyst via pyrolysis temperature regulation. The optimal N-GE at 400 °C exhibited the highest active N content (12.2 wt.%) and H2O2 selectivity (85.45 %) and spontaneous OH production (19.42 μM), achieving a high phenol degradation (93.58 %) at 180 min in neutral pH condition. Importantly, a simple catalyst regeneration method and mechanism was disclosed. It is proposed that the conversion of graphite N and pyridinic N in N-GE plays an important role in oxygen reduction reaction (ORR) and OH conversion, while the conversion of pyridinic N-oxide to pyridinic N is critical to catalyst stability and sustainability. This study provides a new insight into structure design of electro-catalyst about stability of nitrogen-doped carbon materials for efficient H2O2 generation and cost-effective pollutants removal.

Spin-dependent band-gap driven by nitrogen and oxygen functional groups in zigzag graphene nanoribbons

We investigated the role of nitrogen and oxygen functional groups on the electronic and magnetic properties of zigzag graphene nanoribbons (ZGNRs) using spin-polarized first-principles density functional theory calculations. Twenty four functional groups of nitrogen, oxygen, and nitrogen-oxygen configurations were attached to the edge of ZGNRs. We analyze the band structure, spin-resolved bandgap, charge transfer, magnetic ordering, and binding energy. Similar to the pristine ZGNR, an indirect bandgap semiconducting behavior dominated in functionalized ribbons, except for carbonyl, pyrane, and pyridinium groups, that displays a metallic behavior. Spin-resolved band gap calculations revealed a strong dependence on the functional groups. Carbonyl groups showed a half-metallicity behavior with only spin up states at the Fermi level. In general, the functionalized ribbons displayed ferromagnetic alignment along the edges, but antiferromagnetic alignment between them, resulting in a total null magnetization. We showed some exceptions, the carbonyl, pyrane, lactam, pyridine N-oxide, and pyridinium functional groups induced significant changes in the magnetic arrangement, not only along the edge where they were attached but also to the opposite side. We have also incorporated a pentagon-heptagon pair or a single pentagon defect at the edge to explore the quinone, pyrone, and pyridone functional groups.

A Cephalosporin Prochelator Inhibits New Delhi Metallo-β-lactamase 1 without Removing Zinc.

Antibacterial drug resistance is a rapidly growing clinical threat, partially due to expression of β-lactamase enzymes, which confer resistance to bacteria by hydrolyzing and inactivating β-lactam antibiotics. The increasing prevalence of metallo-β-lactamases poses a unique challenge, as currently available β-lactamase inhibitors target the active site of serine β-lactamases but are ineffective against the zinc-containing active sites of metallo-β-lactamases. There is an urgent need for metallo-β-lactamase inhibitors and antibiotics that circumvent resistance mediated by metallo-β-lactamases in order to extend the utility of existing β-lactam antibiotics for treating infection. Here we investigated the antibacterial chelator-releasing prodrug PcephPT (2-((((6R,7R)-2-carboxy-8-oxo-7-(2-phenylacetamido)-5-thia-1-azabicyclo[4.2.0]oct-2-en-3-yl)methyl)thio) pyridine 1-oxide) as an inhibitor of New Delhi metallo-β-lactamase 1 (NDM-1). PcephPT is an experimental compound that we have previously shown inhibits growth of β-lactamase-expressing E. coli using a mechanism that is dependent on both copper availability and β-lactamase expression. Here, we found that PcephPT, in addition to being a copper-dependent antibacterial compound, inhibits hydrolysis activity of purified NDM-1with an IC50 of 7.6 μM without removing zinc from the active site and restores activity of the carbapenem antibiotic meropenem against NDM-1-producing E. coli. This work demonstrates that targeting a metal-binding pharmacophore to β-lactamase-producing bacteria is a promising strategy for inhibition of both bacterial growth and metallo-β-lactamases.

Synthesis and investigation of enhanced luminescence of Ln(III)-complexes containing fluorinated β-diketone and oxygen donor ancillary ligands for efficient advanced displays

2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (fod) fluorinated β-diketone had been used to prepare a series of Ln3+ (Eu or Tb) ternary complexes with monodentate ancillary ligands such as aqua, urea, triphenylphosphineoxide (TPPO) and pyridine-N-oxide (PNO). Prepared ternary materials Eu(fod)3.(aqua)2 (1), Tb(fod)3.(aqua)2 (2), Eu(fod)3.(urea)2 (3), Tb(fod)3.(urea)2 (4), Eu(fod)3.(TPPO)2 (5), Tb(fod)3.(TPPO)2 (6), Eu(fod)3.(PNO)2 (7), Tb(fod)3.(PNO)2 (8) were illustrated through various structural and photo-physical spectroscopic practices. Emission measurement showed characteristics strong emission in red aa well as green spectral region accredited to the electric dipole 5D0→7F2 and 5D4→7F5 hypersensitive transitions of Eu3+ and Tb3+ ions respectively. An inclusive comparative investigation of enhancement features in the luminescence intensity had been carried out to determine the role of ancillary ligands. Improved luminosity was achieved as auxiliary ligands not only substituted the solvent molecules in coordination sphere but also indirectly sensitize metal ion through transfer of energy to emissive level of respective Ln3+ ion from triplet state of ligand. Decay curve specified uniformity in chemical environment around central metal ion. Efficient red and green light materials could be successfully used for fabricating OLEDs.

Synthesis and characterization of penta-coordinated 2- and 4-substituted pyridine N-oxide silicon complexes

Novel penta-coordinated 2- and 4-substituted pyridine N-oxide silicon complexes were synthesized by the reaction of various 2- and 4-substituted pyridine N-oxides with silicon pinacolate. These complexes were characterized by 29Si NMR, 1H NMR and 13C NMR spectroscopy. The objectives of the present work is the study of influence of substitution at either 4 or 2-position of the pyridine N-oxide on the effect of the profile of pentacoordination.

Catalytic Deoxygenation of Amine and Pyridine N-Oxides Using Rhodium PCcarbeneP Pincer Complexes

Rhodium PCcarbeneP pincer complexes 1-L (L = PPh3, PPh2(C6F5), PCy3) readily facilitate deoxygenation of amine and pyridine N-oxides. The resulting complexes exhibit η2-C═O coordination of the resulting keto POP pincer ligand. These η2-C═O linkages in the metalloepoxide complexes are readily reduced by isopropyl alcohol and various benzylic alcohols. Thus, efficient catalytic deoxygenation of amine and pyridine N-oxides is possible using complexes 1-L and isopropyl alcohol. This represents a pioneering example of PCcarbeneP pincer complexes being used as catalysts for catalytic deoxygenation.

Photocatalytic oxidative desulfurization and denitrogenation for fuels in ambient air over Ti3C2/g-C3N4 composites under visible light irradiation

MXene Ti3C2 modified g-C3N4 composites were prepared and used in photocatalytic oxidative denitrogenation and desulfurization under visible light. The photocatalysis system adapted to oxidation of small molecular pyridine and thiophene for fuels in the ambient air without adding extra H2O2 or pure O2 oxidants. Structural and photoelectric properties of the photocatalysts were characterized and compared. In an optimal composite, g-C3N4 nanosheets were successfully intercalated by Ti3C2 layers to form an interfacial effect and heterojunction. Intercalation effect accelerated the photogenerated electrons transferring from g-C3N4 to Ti3C2, and inhibited the recombination of electron-hole pairs. Ti3C2/g-C3N4 composite exhibited enhanced photocatalytic performance, high mineralization efficiency, and good recyclability in the removal of pyridine and thiophene. Mechanism and DFT studies proposed that the holes acted as the major active species for the photocatalysis procedures to form the reactant intermediates, while the electrons and O2 generated superoxide radicals provided a promotion effect on the final conversions.

Efficient Tosylation of Dihydroxybenzenes in a Two-Phase Water–Dichloromethane System

The effect of the structure of the catalyst and the type of base on the reaction rate and product yield of the tosylation of dihydroxybenzenes in a two-phase water–dichloromethane system in the presence of pyridine N-oxide derivatives was demonstrated. It was found that with 4-dimethylaminopyridine N-oxide and potassium carbonate it is possible to obtain dihydroxybenzene tosylates with yields of more than 90%.

Adsorption and Reactions of 3-Bromopyridine and 2-Bromopyridine on Cu(100) and O/Cu(100)

Adsorption and reactions of 3-bromopyridine and 2-bromopyridine on Cu(100) and O/Cu(100) have been investigated, attempting to explore the chemical processes by identifying a variety of possible reaction intermediates and products, such as bipyridine, pyridyne, pyridine, pyridine oxide, hydroxypyridine, pyridone, and so forth. They can be generated from the Ullmann reaction, dehydrogenation, hydrogenation, hydroxylation, and oxidation of pyridyl groups on the surfaces. Temperature-programmed reaction/desorption, reflection–absorption infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations have been employed for this research. At a monolayer coverage of 3-bromopyridine on Cu(100), a perpendicular 3-pyridyl is generated on the surface below 300 K because of the C–Br bond scission. This surface species undergoes loss of hydrogen, hydrogenation, and ring rupture at ∼450 K. The first two processes result in the pyridine formation. The dissociated fragments continue to react to form H2, HCN, and (CN)2 at higher temperatures. The relative amounts of the products of pyridine, H2, HCN, and (CN)2 are dependent on the coverage of 3-pyridyl. In the presence of surface oxygen atoms (O(ad)), dissociation of 3-bromopyridine also generates 3-pyridyl first. However, the pyridine formation from this intermediate is terminated, with decreased H2, HCN, and (CN)2. Additional products of H2O, CO, CO2, and HNCO are generated. For 2-bromopyridine (1.0 L) on Cu(100), at a coverage slightly higher than a monolayer, a perpendicular 2-pyridyl is generated below 300 K, and its decomposition generates pyridine (∼525 K), together with H2, HCN, and (CN)2 at higher temperatures. At a large exposure of 10.0 L of 2-bromopyridine, additional pyridine is generated at 650 K, which is suggested to be originated from an electronically/structurally strongly perturbed C5NH4 intermediate. On O/Cu(100), no 2-pyridyl intermediate is measured from the primary 2-bromopyridine decomposition; however, 2-oxypyridine is formed instead. This intermediate can be produced from nucleophilic attack on the 2C atom of 2-bromopyridine by O(ad) and/or from recombination of 2-pyridyl and O(ad). The 2-oxypyridine further reacts to form H2O, HCN, CO, CO2, HCNO, and (CN)2.

Cambiarenes: Single-Step Synthesis and Selective Zwitterion Binding of a Clip-Shaped Macrocycle with a Redox-Active Core.

A novel macrocyclic host molecule was synthesized that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, it is redox-active. Host-guest binding involving the clip-shaped cavity indicates selective binding of pyridine N-oxides based on the electron density of and steric bulk around the anionic oxygen.

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review.

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks.

Structural Disorder in High-Spin {CoII9WV6} (Core)-[Pyridine N-Oxides] (Shell) Architectures.

The combinations of Co(II), octacyanidotungstate(V), and monodentate pyridine N-oxide (pyNO) or 4-phenylpyridine N-oxide (4-phpyNO) led to crystallization of novel crystalline phases {CoII[CoII8(pyNO)12(MeOH)12][WV(CN)8]6} (1) and {CoII[CoII8(4-phpyNO)7(MeOH)17][WV(CN)8]6}·7MeOH·(4-phpyNO)3 (2). In both architectures, metal–cyanide clusters are coordinated by N-oxide ligands in a simple monodentate manner to give the spherical objects of over 1 nm core diameter and about 2.2 nm (1) and 3 nm (2) of the total diameter, terminated with the aromatic rings. The supramolecular architecture is dominated by dense and rich π–π interaction systems. Both structures are characterized by a significant structural disorder in ligand shell, described with the suitable probability models. For 1, the π–π interactions between the pyNO ligands attached to the same metal centers are suggested for the first time. In 2, 4-phpyNO acts as monodentate ligand and as the crystallization molecule. Magnetic studies indicate the high-spin ground state due to the ferromagnetic interactions Co(II)–W(V) through the cyanido bridges. Due to the high symmetry of the clusters, no signature of slow magnetic relaxation was observed. The characterization is completed by solid-state IR and UV–Vis–NIR spectroscopy. The conditions for the stable M9M’6-based crystals formation are synthetically discussed in terms of the type of capping ligands: monodentate, bridging, and chelating. The potential of the related polynuclear forms toward the magnetism-based functional properties is critically indicated.

Visible-Light-Promoted C2 Selective Arylation of Quinoline and Pyridine N-Oxides with Diaryliodonium Tetrafluoroborate.

A protocol of visible-light-promoted C2 selective arylation of quinoline and pyridine N-oxides, with diaryliodonium tetrafluoroborate as an arylation reagent, using eosin Y as a photocatalyst for the construction of N-heterobiaryls was presented. This methodology provided an efficient way for the synthesis of 2-aryl-substituted quinoline and pyridine N-oxides. This strategy has the following advantages: specific regioselectivity, simple operation, good functional group tolerance, and high to moderate yields under mild conditions.

Synthesis of cobalt doped mesoporous silica by using the rice husks as both silicon source and template with its catalytic oxidation of 2-methyl pyridine

Cobalt doped mesoporous silica (Co-SiO2) was prepared using the rice husks as both silicon source and template. Structural characterization of the catalysts was done by various techniques, such as Xray diffraction, FT-IR, N2 adsorption/desorption, and scanning electron microscopy. Co-SiO2 was used as a catalyst for the oxidation of 2-methyl pyridine and exhibited high substrate conversion (94.6%) and good product (2-pyridinecarboxylic acid) selectivity (92.4%). It even exhibited higher selectivity than Co-MTiO2, Co-MCM-41, Co-SBA-15. Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one and it can be reused with almost the same activity.

Synthesis of 3-(2-quinolyl) chromones from ynones and quinoline N-oxides via tandem reactions under transition metal- and additive-free conditions.

A novel method for the synthesis of 3-(2-quinolyl) chromones through a tandem [3+2] cycloaddition/ring-opening/O-arylation from ynones and quinoline N-oxides has been developed. This protocol proceeds under transition metal- and additive-free conditions and can be amplified to the gram level in 91% yield. 3-(1-Isoquinolyl) and 3-(2-pyridyl) chromones are also successfully synthesized using isoquinoline and pyridine N-oxides under basic conditions. Various heteroarene-contaning chromones were afforded in 30-98% yields, which are difficult to be obtained and are compounds of interest in pharmaceutical chemistry and chemical biology.

Aerobic C(sp3)–H oxidation and oxygenation of quaternarized quinolines and pyridines by visible-light-induced photocatalysis

One stone two birds: two kinds of oxygenation products (>60 new products) including carboxylate inner salts and alcohols have been accessed under mild aerobic photocatalysis.

Recyclable anhydride catalyst for H2O2 oxidation: N-oxidation of pyridine derivatives.

The catalytic efficiency and recyclability of poly(maleic anhydride-alt-1-octadecene) (Od-MA) and poly(maleic anhydride-alt-1-isobutylene) (Bu-MA) were evaluated for use in the development of a metal-free, reusable catalyst for the oxidation of pyridines to pyridine N-oxides in the presence of H2O2. The Od-MA catalyst was easily recovered via filtration with recovery yields exceeding 99.8%. The catalyst retained its activity after multiple uses and did not require any treatment for reuse. The Od-MA and H2O2 catalytic system described herein is eco-friendly, operationally simple, and cost-effective; thus, it is industrially applicable. Od-MA and H2O2 could potentially be used in place of percarboxylic acid as an oxidant in a wide range of oxidation reactions.

Further, Small-Molecule Pyrolysis Products Derived from Chitin

In an ongoing study of the products formed on pyrolysis of chitin (4) under a range of conditions, we now detail the isolation and characterisation of the crystalline and hitherto undetected pyridine N-oxide 18 and enamide 19. Pathways for the formation of these products have been proposed and subjected to both experimental and computational assessment.